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Handling image sensors -- CMOSIS CMV-AN03-v03

Modified on: Wed, Aug 30, 2017 at 11:24 AM

INTRODUCTION

This document will describe general procedures and practices best used when handling the CMOSIS standard product image sensors. As all integrated circuits, image sensors are sensitive to ESD. ESD can cause both hard ESD damage and soft ESD damage. Hard ESD damage will result in the immediate damage of the circuit and the circuit will not be functional anymore, or only partly functional. Soft ESD damage can result in changing characteristics and/or reduced lifetime of the circuit. The implementation of an effective ESD control program is an investment which pays itself. The ESD protection requirements below are based on JEDEC standard JESD625A and CMOSIS recommends JESD625A as baseline for successful prevention of ESD damage.

SPECIAL MEASURES FOR OPEN IMAGE SENSORS

Open image sensors (without glass lid) are very sensitive to bond wire damage and sensor contamination. Therefore the following applies when handling open image sensors:

Special care should be taken to avoid touching the bonding wires

Always handle open sensors in a clean room environment

Cleaning is possible, but difficult. Only local cleaning (with cotton tip and IPA) is suitable for open sensors. Blowing off particles is possible, but care should be taken not to damage the bonding wires by using too much air/N2 pressure

If possible, intermediate storage should be done facing down to avoid contamination

If possible, temporary protection (like a temporary glass lid) should be used to protect the open image sensor

DEVICE HANDLING

As image sensors are sensitive to particle contamination, specific measures need to be taken when handling image sensors:

Image sensors are preferable handled in a clean environment like a clean room or a laminar flow bench.

Always use effective ESD protection (see section 2.2)

Always handle image sensors wearing gloves that are both ESD safe and clean. Use the right size of gloves to avoid contacting the image sensor glass lid with the finger tips.

Always use mouth protection to avoid saliva or other contamination. Saliva are known to be very difficult to clean, especially on surface coatings like AR and IR coating

If the glass lid is contaminated, it should be cleaned as explained in section 4.3.

CLEANINGWhen cleaning image sensors, the ESD protection and handling requirements apply. Cleaning of the glass lid should always be avoided as one can never get a perfectly cleaned glass lid. If cleaning needs to be done, several methods can be used depending on the type and severity of the contamination. Ultrasonic cleaning is not appropriate due to the risk of damaging the image sensor.

BLOW OFF

Blowing off can be used to remove loose particles. The following applies when blowing off particles:

Blow off particles can be done using clean nitrogen or ionized dry compressed air.

The cleanliness of the N2/air and the equipment (air gun/N2 gun) is essential for a good result.

Never blow towards other sensors

When working under a flow bench, always blow out of the bench

WET WIPING

Wiping can be used to remove loose particles, fixed particles and surface contamination. The following applies when wiping glass lids:

Always use wet wipes for cleaning the glass lid. The use of an ESD protective wipe is preferred; however some ESD protective wipes are not to be used as they easily scratch surface coatings like AR and IR coatings.

Use IPA (Isopropyl Alcohol) as cleaning fluid. Other fluids (like acetone or methanol) are not preferred as they can contaminate the glass lid, degrade the glass lid attachment or etch the surface coating. Some fluids are known to be very toxic.

Wipe gently in one direction and avoid wiping again with the same part of the wipe

Avoid contamination of the IPA in the bottle by not dipping the wipe using the bottle. Always use a small intermediate canister.

Using too much IPA might leave stains, using not enough IPA might cause small scratches.

If the glass lid cannot be cleaned in 3 attempts, it might be damaged or the contamination cannot be removed.

LOCAL CLEANING

Local cleaning can be done using cotton tips and IPA. The following applies when cleaning glass lids locally:

Always use wet cotton tips for cleaning the glass lid.

Use IPA (Isopropyl Alcohol) as cleaning fluid. Other fluids (like acetone or methanol) are not preferred as they can contaminate the glass lid, degrade the glass lid attachment glue or etch the surface coating. Some fluids are known to be very toxic.

Wipe gently in one direction and avoid wiping again with the same cotton tip

Avoid contamination of the IPA in the bottle by not dipping the cotton tip in the bottle. Always use a small intermediate canister.

Using too much IPA might leave stains, using not enough IPA might cause small scratches.

If the glass lid cannot be cleaned in 3 attempts, it might be damaged or the contamination cannot be removed.

EXCESSIVE LIGHTExcessive light falling on the sensor can cause heating up the micro lenses and color filters. This heat can cause deforming of the lenses and/or deterioration of the lenses and color filters by making them more opaque, increasing the heat up even more. Avoid shining high intensity light upon the sensors for extended periods of time. In case of lasers, they can cause heat up but can also damage the silicon die itself.